What are their benefits to a foreign society? I’ve yet to see that delineated.
You start by trying to explain it by “who benefits,” but that’s not enough, since all kinds of irrational actions have been taken by political leaders throughout the ages.
Of more importance than the mundane “who benefits” in this case, I think there is a left-wing religion of globalism and socialism that dictates that this happen.
It’s been centuries in the making, and this is just its latest manifestation.
So even though there may be perceived political advantages to left-wing parties to let this happen, I think the secular religious aspect of it is the most important driver.